How to Make It
Set up your grill for indirect grilling and light it.
Brush the salmon skin with the sesame oil. Generously season the salmon on both sides with salt and pepper and set it on the cedar plank skin side down.
In a medium bowl, whisk the miso with the mayonnaise, sugar, lemon zest and white pepper (see Note). Spread the miso glaze evenly over the salmon. When the fire is moderately hot, set the plank in the center of the hot grate, away from the heat, and cover the grill. Cook the salmon for 20 to 30 minutes, until the fish is pink pink throughout and the glaze is golden. To test for doneness, insert a slender metal skewer in the side of the fillet for 20 seconds; it should be very hot to the touch. Transfer the salmon on the plank to a heatproof platter and serve at once.
If the miso glaze is very thick, thin it with 1 to 2 tablespoons of warm water, sake or mirin.